I have a 15 Rl-P in a ported, 2.75cft, tuned to 30hz, getting 1000 watts. It replaced a JL 15W6 in the same box. The Rl-P kills the W6 in SQ and SPL, no comparison.
I also had 2 12 JLW6V2's, sealed and ported(3.5cft, 28hz). I would say that the Rl-P is a little bit louder than the 12's ported, and very very close in SQ although I do give the SQ edge to the W6V2's.